This present invention relates generally to the field of chlorine detection, and specifically relates to a method for measuring chlorine content in automated analyzers.
The requirement to provide chlorine analyzers with additional reagents has long been a concern. There exist a number of commercially available residual chlorine analyzers. Current thinking in the industry is that in order to obtain accurate measurements of chlorine levels in water, the chlorine must be in the form of HOCl. Further, it is believed that in order to obtain this electroreducible species, the pH of the sample containing chlorine must be lowered to a pH of about 4.5 to 5, or lower. However, the reagents required to lower the sample pH have several undesirable side-effects. In applications where no drain is available, the measured sample is often discharged onto the ground, which can result in a buildup of a reagent which is often a nutrient and consequentially facilitates a large biological growth. The nutritive nature of the buffers used to date also gives rise to biological growth in the analyzers, potentially fouling electrodes and clogging portals so that more frequent and costly preventative maintenance is required.
Many of the reagent systems studied are based on organic acids. Some of the most readily available aqueous acid systems require the addition of a weak acid salt to create a buffer in order to stabilize the reagents for shipping and storage. Some of the more commonly used systems include phthalate, succinate, acetate, phenylacetate, citrate, phosphate, oxylate, and salicylate. All of these are believed to be biological nutrients, and as such, may cause problems in the growth and contamination of feed lines and storage containers. Some of the less common systems include amine-based buffers derived from substituted glycines and taurines. Taurine based buffers are often substituted for borate buffers in biological systems. Although they are reported to be resistant to enzymatic and non-enzymatic degradation, the organic nature of the compound still makes these acids a probable biological nutrient.
There is a large interest in lessening the disposal problem and reducing or eliminating the nutrient nature of the added reagent to the chlorine analyzer. A variety of different buffers have been utilized, such as phosphates, but none have been found to be generally acceptable. Alternatives have been considered, including operating the chlorine analyzer without buffers or using different buffers. If no reagent is used, however, serious measurement errors can result.
Furthermore, it is important to consider the cost implications of any chemical reagent system that could replace the acetate system. Even the more common organic acids as listed above can be considerably more expensive than the present one.
There remains a need in the art for better methods that allow for chlorine detection at higher pH levels, are cost efficient, and avoid the problems associated with the addition of nutritive reagents to the chlorinated medium.
In one aspect, the invention provides a method of measuring chlorine content in a solution without lowering the pH of the solution to the acid range by modifying a solution containing chlorine and water to contain a proton donating compound.
In another aspect, the invention provides a method of measuring total chlorine content in an aqueous solution containing a mixture of chloramines without lowering the pH of the solution to the acid range. The method involves adding an iodide salt to an aqueous solution, where the chlorine is present in the aqueous solution as free and combined chlorine, and the steps as described above.
In still another aspect, the invention provides a stable aqueous reagent solution useful in automated chlorine analyzers containing sodium bicarbonate, a base that increases the pH to above about 9.0 without significantly affecting the ability of the sodium bicarbonate to donate protons when mixed with a chlorine solution, and water. A stable aqueous reagent solution containing sodium tetraborate decahydrate, water, and an acid to adjust the pH of the solution to about 6.8 can also be used.
In yet a further aspect, the invention provides an apparatus for detecting the level of chlorine in a water sample. The apparatus includes a cartridge having a solid proton donating compound, an inlet port connected to a water sample supply, and an outlet port in communication with an automated chlorine detector. The inlet and outlet ports of the cartridge are appropriately spaced so that the water sample which flows through the cartridge dissolves the solid proton donating compound. Thereafter, the water sample which contains the dissolved compound is supplied to the automated chlorine detector.
In still another aspect, the invention provides a method of detecting chlorine in an automated chlorine detector using the apparatus as described above.
In another aspect, the invention provides a standpipe apparatus for use in detecting the level of chlorine in a water sample. The standpipe is connected to a supply of water sample and is capable of containing an amount of the sample such that a standpipe water level and a standpipe headspace are defined. The standpipe has an outlet which is adjacent the water lever and which supplies a flow of water sample to a chamber of an automated chlorine detector. The standpipe has another outlet which is spaced below the water level and which feeds a flow of water sample to a cartridge which contains a solid proton dissociating compound and which has a larger volume than the standpipe. The water sample which flows through the cartridge dissolves the compound and is fed into a mixing chamber in the chlorine detector. In addition, the apparatus can include means for adding iodide to the sample water in the standpipe.
In still another aspect, the invention provides a method of detecting chlorine in an automated chlorine detector using the apparatus above.
Other aspects of the invention are described further in the following detailed description of the preferred embodiments thereof